1. Field of the Invention
The present invention relates to a liquid supply pump unit for flowing a culture liquid used for plant culture and a hydroponic culture apparatus using this liquid supply pump unit and, more particularly, to a liquid supply pump unit switch generates a water flow in a culture liquid by utilizing the air supply operation of an air supply pump used for replenishing oxygen dissolved in the culture liquid and which utilizes a solar battery as a drive power supply for this air supply pump, and a hydroponic culture apparatus using this air supply pump unit.
2. Description of the Prior Art
Hydroponic culture is a method of culturing plants not by using soil but by supplying components necessary for plant growth with an artificially adjusted culture liquid. In hydroponic culture, to supply the culture liquid to the plant, various types of methods are employed, e.g., a liquid level change method of changing the liquid level of the culture liquid, a flow method of circulating a culture liquid, a spray method of spraying a culture liquid to the plant root, and the like.
In hydroponic culture, nutrient components necessary for plant growth must be sufficiently supplied to the culture liquid. In addition, it is very important to supply a sufficient amount of oxygen to the plant root in order to promote the normal growth of the plant without rotting the root. To supply a sufficient amount of oxygen to the root, a sufficient amount of oxygen may be dissolved in the culture liquid to increase the dissolved oxygen concentration. Also, it is effective to flow the culture liquid.
In Japanese Examined Patent Publication No. 5-25448, the present inventors disclose a hydroponic culture apparatus using the liquid level change method. In this hydroponic culture apparatus, air is supplied from an air supply pump into a culture liquid to dissolve oxygen in the culture liquid, thereby increasing the amount of oxygen dissolved in the culture liquid. Also, a partition member formed in a culture liquid tank is temporarily charged with the supplied air. The reserved air in the partition member is intermittently discharged into the culture liquid to change the liquid level of the culture liquid, thereby flowing the culture liquid. When the liquid level is lowered, the plant root is brought into direct contact with air, thereby supplying oxygen to the root. However, according to this apparatus, depth of the culture liquid tank may be 25 cm to 30 cm and relatively much quantity of the culture liquid is necessary.
According to a conventional method of increasing the amount of dissolved oxygen by dissolving oxygen in the culture liquid (this will be called "oxygen enrichment" hereinafter), air is supplied into the culture liquid by using an air supply pump and is discharged into the culture liquid in the form of small bubbles, thereby performing oxygen enrichment. According to a conventional method of supplying the culture liquid to the plant, the culture liquid is supplied into a culture tank by using a liquid supply pump, and a culture liquid flow is generated and flowed in the culture tank. According to these methods, the air supply pump and the liquid supply pump must always be operated, increasing the cost.
In particular, since the liquid supply pump for generating a water flow requires a large power consumption, a plurality of culture tanks are connected to one liquid supply pump, and the water flow directions are switched to generate a water flow in each culture tank. Also, the operation of the liquid supply pump during the nighttime is cut off. However, a selector for switching the water flow, a controller for changing the operation contents between the daytime and the nighttime, and the like become additionally necessary, leading to an increase in equipment cost.
The plant activity and a change in quantity of light substantially correspond to each other. When the quantity of light increases, the necessary oxygen amount also increases accordingly. The operation amount of the air supply pump preferably increases accordingly. In order to perform a control operation in accordance with the quantity of light in this manner, a sensor for detecting the quantity of light irradiated on the plant and other controllers become necessary, leading to an increase in equipment cost.